Mixing circuit



NOV. 2, 1954 FEMMER 2,693,533

MIXING CIRCUIT Filed Dec. 4, 1951 2 Sheets-Sheet l OUTPUT FIG. I I4 20 FIG. 3

C 2! I I I I I I I I F I l I I 1 I I l l I l I I I I I I I I I I l I 22 I I I FIG. 4

CONTROL 7 FIG. 2

CONDITION l CONDITION 2 CONDITION 3 SW28 ON 29 swso 0N 4o L f II swza ON 29 I swzo ON 41 SW 28 ON 34 m CATHODE------------------------ CONTROL PULSES OUTPUT INVENTOR MAX E. FEM R W AGENT CONTR FIG.6

1954 M. E. FEMMER 2,693,533

MIXING CIRCUIT Dec. 4, 1951 2 Sheets-Sheet 2 OUTPUT PIC-3.5

CONTROL INVENTOR MAX E. FEMMER AGENT United States Patent Ofifice 2,693,533 Patented Nov. 2, 1954 MIXING CIRCUIT Max E. Femmer, Hopewell Junction, N. Y., assignor to International Business Machines Corporation, New York, N. Y., a corporation of New York Application December 4, 1951, Serial No. 259,745

9 Claims. (Cl. 250-27) This invention relates to mixing circuits in general and to mixing circuits employing diodes in particular.

An ob ect of the invention is to provide a voltage wave mixing crcuit adapted to merge voltage waves appearing on a pair of input terminals into a. single output terminal.

Another object of the invention is to provide a mixing circuit which is adapted to provide an output impulse whenever either input voltage wave exceeds a predetermined amplitude.

A further object of the invention resides in the provision of means for presenting a uniform impedance load to both the input terminals.

Another feature of the invention resides in the provision of a voltage limiter adapted to maintain a constant output voltage when the input voltage thereto widely varies in amplitude.

Yet another feature of the invention resides in the provision of means for rapidly switching the mixing circuit on and off without disturbing the impedance relations therein.

Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose, by way of example, the principle of the invention and the best mode, which has been contemplated, of applying that principle.

In the drawings:

Fig. l is a wiring diagram of the diode mixing circuit.

Figs. 2 and 3 are charts illustrating the operating characteristics of the mixing circuit.

Fig. 4 is a wiring diagram of an alternative control circuit.

Fig. 5 is a modification of the circuit of Fig. 1 to produce pulses of positive polarity in the output terminal.

Fig. 6 is a modification of the circuit of Fig. 1 wherein crystal diodes are employed in lieu of vacuum tube diodes.

Referring to Fig. 1 the signals to be combined are impressed upon input terminals 10 and 11 each connected respectively through condensers 12 and 13 to the diode rectifiers 14, 15, 16 and 17. Resistors 18 and 19 respectively are connected from the diode rectifier input terminals to ground thereby providing a shunt for the same.

The cathode of diode 14 is connected to the plate of diode and to the junction of condenser 12 and resistor 18 above-mentioned. The plate of diode 14 is connected to the output terminals 20 and to a resistor 21, the other end of which is grounded. Similarly, the plate of diode 16 is connected to the output terminal 211 and resistor 21. The cathode of diode 16 and the plate of diode 17 are connected together and to resistor 19.

The cathodes of diodes 15 and 17 are connected together through resistors 22 and 23 connected in series relation. The junction of resistors 22 and 23 is connected to the output 20 via a resistor 24.

The cathodes of diodes 15 and 17 are also connected to ground respectively via resistors 25 and 26.

At the junction point of resistors 22, 23 and 24, a wire 27 is taken off leading to a single pole double throw switch 28. Pole 29 of said switch is connected to one terminal 31 of a double pole double throw switch 30. The other terminal 32 of switch is connected to ground. Swith 30 is adapted to be used as a polarity reversing device for applying, when thrown to the left hand position, a negative bias from battery 33 to the cathodes of diodes 15 and 17 through switch 28. Conversely, when switch 30 is thrown to its right hand position a positive bias is applied to the diodes.

The other terminal 34 of switch 28 is connected directly to the cathode of tube 35 and resistor 36 is connected from the cathode of tube 35 to ground. Tube 35 is adapted to operate as a cathode follower having resistance 36 as its load, and consequently, the plate thereof is connected directly to a source of positive high voltage (not shown). The grid of cathode follower tube 35 is connected to a terminal 37 to which are applied control impulses graphically illustrated in Fig. 2 from a source which is not a part of this invention and consequently is not shown. A source of bias 38 is applied between ground and the grid of tube 35 via a resistor 39 and is eilective to hold the grid below the cutoff point during periods when no control signals are applied to terminal 37. in an embodiment of the circuit tubes 14 and 15, 16 and 17 may be of the dual diode type 6AL5 with both diodes enclosed in a single envelope. Alternatively, germanium crystal diodes, for example, type 1N54A, may be used in place of a vacuum tube diode, see Fig. 6.

An essential feature of the invention resides in the ratio of resistors 18 and 19 to each of resistors 21, 22, 23, 24, 25 and 26. In the preferred embodiment this ratio is of the order of l to 2 although, to secure other output etiects it will be understood that other ratios may be used. For example, resistors 21, 25 and 26 may be made equal to one another but have values different from the other resistors beforementioned. To further illustrate, resistors 18 and 19, labelled A may have a magnitude of 10,000 ohms while the other resistors, labelled B and C may be made equal to each other and have a magnitude of twice this amount.

The operation of the circuit will now be described. Assume that switch 28 is so thrown that terminal 29 is connected to wire 27 and that switch 30 is thrown tothe left connecting the positive pole of the battery 33' to ground through terminals 32 and 40 and the negative pole to line 27 through terminals 31 and 10 thereby causing a negative bias of approximately -5 volts, when battery 33 supplies a potential of 20 volts, to be imposed upon the cathodes of diodes 1.5 and 17 via resistors 22 and 23, and also applying a potential of -10 volts to the anodes of diodes 14 and 16 over resistor 24.

Thus, referring to Fig. 2 the effects of such switching is shown under condition 1. The input signals applied to terminals 10 and 11 are generally of push-pull characteristics, although of course, signals of other phase relationship may be used.

If the first signal impulses aplied to inputs it) and 11 are coincident in time but opposite in phase diode 16 would conduct when the amplitude of the signal applied to the cathode was more negative than the anode and an output voltage would appear across resistor 21. Diode 15 would conduct immediately upon application of the positive going pulse on terminal 10 and for the duration of the pulse. The creation by this pulse of a voltage across resistor 25 has no effect on the output.

On the next alternation of input pulses input 10 is driven negative While input 11 goes positive. Consequently when the negative amplitude of the pulse applied to input 10 exceeds the negative bias applied to the anode of diode 14, said tube conducts producing a negative going voltage pulse across resistor 21 at the output terminal 20.

Pulses of positive polarity on the output terminal may be produced by throwing switch 30 to the right so as to connect the positive battery terminal to wire 27 and by reversing the diodes as alternatively shown in Fig. 5. The circuit then operates to permit clipping of the tops of input square wave pulses. For example, under condition 2 shown in Fig. 2, diodes 14A and 16A will now have a positive bias potential applied to their cathodes and while diodes 15A and 17A will also have a positive potential applied to their anodes. Arrival of a positive going impulse at input terminal 10 will cause diode 15A to conduct until the potential on the cathode equals the potential on the anode. Diode 14A will start to conduct when the applied anode potential exceeds the cathode potential. On the next phase of the input signal a negative going impulse will be presented to diodes 16A and 17A from terminal 11. Diode 17A will immediately start to conduct for the duration of the impulse while diode 16A will not be rendered conductive at all.

In order to automatically condition the mixing circuit under control of impulses (condition 3Fig. 2) generated by equipment now shown, switch 28 may be thrown to the position connecting terminal 34 with wire 27. Terminal 34 is connected directly to the cathode of tube 35 having its control grid biased to a negat ive voltage beyond cutoff. Application of a positive-going control impulse on terminal 37 of a magnitude greater than the potential supplied by battery 38 would have the effect of rendering tube 35 conductive and thereby causing a positive potential to be produced across resistor 36 between switch terminal 34 and ground. The value of resistance 36 may be so adjusted that the potential developed across same is equal to that supplied by battery 33 and will have the same elfect upon the diode circuits as does the battery when its positive pole is connected to wire 27. Also by adjusting the value of the bias voltage produced it is possible to select any fraction of the input signal for transmission to the output terminal.

Fig. 4 shows one version of how tube 34 may be connected so as to coact with resistor 36 in producing a negative bias condition equivalent to that shown in condition 1 of Fig. 2.

Fig. 3 is presented to show output conditions for oppositely phased sinusoidal input voltages under conditions when a negative potential is used for bias.

In order to present uniform load impedance to the input condensers 12 and 13, a pair of diodes is needed for each condenser. If the example of condition 1 is considered where a positive pulse is applied to terminal and a negative pulse to terminal 11, it will be seen that diode will be rendered conductive immediately and remain so until the anode voltage approximately equals the cathode voltage. At this time diode 14 will be rendered conductive, diode 15 is cut off. Such a seesaw condition about the bias voltage levels obtains during the application of the input waves and hence the load placed upon input condenser 12 will be constant for the duration of an input pulse even through the transition point at the bias voltage level when one diode ceases conduction and the other starts.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art, without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. A mixing circuit comprising a pair of input terminals for accepting signals to be transmitted to a common output terminal, a first pair of diodes connected in series relation with a resistor between a ground and said output terminal, a condenser connecting said first pair of diodes at their junction point to one of said input terminals, a first shunt resistor connected in parallel with said series resistor and one of said diodes, a second pair of diodes connected in series relation with a resistor between ground and said output terminal, a condenser connecting said second pair of diodes at their junction point to the other of said input terminals and a second shunt resistor connected in parallel with said series resistor and one of said second pair of diodes.

2. A mixing circuit of the type set forth in claim 1 wherein said diodes are electron discharge tubes.

3. A mixing circuit of the type set forth in claim 1 wherein said diodes comprise solid state rectifiers.

4. A mixing circuit of the type set forth in claim 3 zivherein said solid state rectifier is a germanium crystal 5. A mixing circuit of the type set forth in claim 1 wherein said shunt resistors are equal and bear a l to 2 resistance ratio to said series resistors.

6. A four terminal network adapted to transmit signals from a pair of input terminals to a pair of output terminals wherein a constant impedance is presented to said input terminals, comprising a first diode and a condenser in series relation connecting one input terminal with one output terminal, a second diode and a series connected resistor connecting the junction of said first diode and said condenser with the others of said input and output terminals, a first shunting resistor connected in parallel with said second diode and series connected resistor, a second shunting resistor paralleling said output terminals having an ohmage ratio of 2 to l with said first shunting resistor, and means for applying a bias potential to each of said diodes over resistances equal in ohmage value to the ohmage of said second shunting resistor whereby said network is adapted to pass input signals below a predetermined amplitude and to limit other signals to said predetermined amplitude.

7. A plural terminal network adapted to combine a plurality of signals arising from different sources in a single output, comprising, in combination, a plurality of input terminals one for each of said different sources, an output terminal, a grounding terminal for completing the circuit paths from said different signal sources to a using device, a plurality of pairs of series connected unilateral current conducting devices joined to each of said inputs through an impedance, at their connection point, conductive means for connecting a like electrode of one of each of said plurality of pairs of unilateral current conducting devices to said output terminal, impedance means shunting said output and grounding terminals, and means acting to impress equal bias potentials to the other electrode of the other device of each of said plurality of pairs of devices.

8. A network adapted to combine a plurality of signals arising from difir'erent sources in a single sink, comprising, m combination, a plurality of input terminals, one for each of said different sources, a single output terminal corresponding to said sink, a plurality of pairs of series connected junction rectifying devices each pair being oined to an input terminal at their common connectron point, means for connecting like electrodes of one of each of said pairs of devices to said output terminal and means for applying equal bias potentials to the other electrode of the other of said pairs of devices.

9. A network adapted to combine a plurality of signals arising from different sources in a single sink, comprising, ll'l combination, a plurality of input terminals, one for each of said different sources, a single output termmal corresponding to said sink, a plurality of pairs of ser 1es connected junction rectifying devices each pair being oined to an input terminal at their common connection point, means for connecting like electrodes of one of each of said pair of devices to said output terminal, means for applying equal bias potentials to the other electrode of the other of said pairs of devices, and means for controlling the application of said bias potential.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,258,732 Blumlein et a1 Oct. 14, 1941 2,466,959 Moore Apr. 12, 1949 2,576,026 Meacham Nov. 20, 1951 2,584,986 Clark Feb. 12, 1952 

